SUMMARY OF THE PROPOSED WORK: 5-Nitroacenaphthene (5-NAc) was demonstrated to be carcinogenic in both rats and mice. Although 1-nitronaphthene (1-NN) and 5-NAc have similar structural features, the former showed no carcinogenic effect in both species. The conventional nitrating agents on acenaphthene produced unavoidable mixtures of 5-NAc as well as 3-NAc. Therefore a synthetic method was developed and pure 5-NAc was obtained. The mutagenic activities of 5-NAc and 1-NN toward S. typhimurium TA98 and TA100 were determined. 5-NAc was a powerful mutagen while 1-NN was inactive in the presence of rat liver homogenate. In the absence of rat liver homogenate 5-NAc still showed mutagenic activity while 1-NN was weakly active. In order to understand more about the structure activity relationship of 5-NAc as compared to 1-NN, in vitro metabolism studies of 5-NAc were carried out using 9000xg rat liver homogenate. Two major metabolites were identified as 1- and 2-hydroxy-5-nitroacenapthene. The mutagenicity of both metabolities were determined and both had mutagenic activities comparable to 5-NAc with and without 9000xg rat liver homogenate. More detailed metabolism studies are currently in progress to fully elucidate the possible metabolic pathways of 5-NAc. Also the metabolism of 1-NN will be compared to that of 5-NAc to understand the structural requirements for the carcinogenic and mutagenic activities of 5-NAc.